Sforno on Genesis 48:4/ספורנו על בראשית מ״ח:ד׳

1ונתתיך לקהל עמים ונתתי את הארץ, at the time Yaakov received this promise all his sons with the exception of Binyamin had already been born, and G’d had already said to me when I left on the way to Charan (in the dream of the ladder) “the land which you lie on I shall give to you and to your descendants.” (28,13) If so, it had been G’d’s intention at that time already to give me a “community of nations, i.e. separate tribes. Seeing that you and your children are my descendants and it is unreasonable to assume that G’d had had only you personally in mind when speaking of קהל עמים, a community of nations, it is clear to me that I have the right to designate both these sons of yours as being part of this concept קהל, i.e. that each of them will become a founding father of one of these tribes which constitute this community of nations.